Homolog Ortholog and Paralog - for my own memory!

I have been confused with these three all the times and tend to forget pretty easily - so I need to write up with my own hand-writing with the good fountain pen.





Homolog -- the origin (ancestral gene)
Speciation -- ortho-
Duplication (same species) -- para-

I think computer algorithms would enable us to answer which gene is originated from which gene. There should be the pattern where the mathematics calculation could be solved and the factors from the environment to demonstrate the relationship.